Tger,
After reading all the different replies this is what I have to say about the issue:
-About having your own equipment... I think that as long as it is equipment used to provide care within your level of training and certification AND it is legal to own it (as a private citizen) in your state: it's fantastic. In today's world (more in your country than anywhere else) there are too many lawyers. I support your enthusiasm and passion. (Once again, as long as you obtained it legally, have all the permits and or licenses needed /required by law).
-About using your own equipment while off duty... I think it is outstanding that you usually carry it (or part o it) in your POVs. Now, if you encounter yourself in an incident while off duty, first activate the emergency system and make sure the proper authorities (LE, EMS, Fire, etc.) are on their way. If this happens in an urban or semi urban area where emergency services respond within proper response-time there is no need for you to provide care beyond the REAL basic stuff (call for help, scene safety, ABC, reassuring the victim, crowd management, etc.). Not getting involved in further care has many reasons besides the legal ones, among them is that by the time you start it (in urban / semi-urban areas) EMS will be already on scene and you will be then in their way. In rural, partially isolated or isolated areas again, activate the emergency system making sure the professionals on duty are on their way. As long as you're trained and certified provide REAL basic care. If you know for a fact that EMS response will be delayed or compromised and you could represent the difference between life and death to the victim(s) then providing care within your training and certification is not a negative thing at all.
My advise about the above, be familiar about the legal considerations involved with your training and certification while both on duty and off duty.
-About having a POV that has the unmistakenly shape/design of an ambulance... One thing is having it as a collector or an emergency vehicles fan. Another one is using it daily for day to day things "just in case" something happens on the way and you're the first one on scene. Then make sure you have done enough in order to not confussing the public. Meaning: think of those members of the public that have no clue about emergency services and how they would react upon seeing your vehicle at an incident (Why an ambulance looks like that? Why its driver isn't in uniform? Why the agency / jurisdiction is not mentioned on it? Why even if it was the first vehicle on scene it wasn't used for Pt transport? etc. etc.).
Some recommendations about the above (assuming you are not interested in having a private ambulance company)... paint it in colors which are unusual for ambulances (including the star of life -what about a star of life in multiple colors?), have "OUT-OF-SERVICE ambulance" written somewhere on each side of it, etc. If your area is rural, partially isolated or isolated and you will use your POV on a "regular" basis, what about becoming part of a CERT (Community Emergency Response Team) or similar programs?
-About transporting a pt. in your POV... (I know you haven't mentioned it but in some replies the possibility was mentioned) I recommend you not to. Not only due to the legal considerations (not an emergency vehicle, you being off duty, what would happen if you get involved in an MVA, illegal imprisonment, kidnaping, etc. etc.) your intension might be the normal and right one but "too many lawyers in the world." Talking about laws... the main reason why we, as professionals, should respect them, follow them and enforce them -whenever possible and applicable- is because the law -ideally- treats everyone equally. Meaning: you might be a passionate, well-intended and responsible individual, HOWEVER if the law allows you to do it, it could allow anybody to do so and other individuals might not be like you. [Also, if you drive it who will ride in the back. -I guess it will be unlikely for you to have your partner while off duty].
-Finally, be sure by all means you are not (unintentionally) impersonating an emergency service worker. This, as R/r911 mentioned, is a serious offense. No matter if you are one at your job, it is a whole different thing when off duty. Check with your employer's legal dept. or with the state heath dept. Nothing wrong with being proud of your job or profession. How many people in today's modern world could say they love what they do? Yes, we are lucky. HOWEVER, one thing is wearing a shirt that mentions what you do, another is wearing a uniform while off duty. -Apply that to POVs. A bumper sticker and a magnetic strobe light is one thing, a former official emergency vehicle with a light bar is another way different one.
In my case, I am a professional lifeguard that except when in the US (4 months a year) I live and work in Argentina. Here both public lifeguard services and private sector employers never provide their lifeguards with proper equipment (mainly due to huge budget problems). In my case I provide services as a self-employed individual and I am planning to create a private company to provide such services in the future. I have my own equipment which with a big effort I have been purchasing very gradually. I do carry it to work in my POV and when off duty I carry part of it 24/7. So far it is not advanced equipment (jump trauma bag, pocket masks, first aid stuff...). I am planning to purchase an AED, BVM and O2 soon. I would only use it while off duty in the case I am in a rural, partially isolated or isolated area since in Argentina EMS is in a chaotic situation.
In Argentina there is a federal law that states off duty lifeguards are the only ones that have a duty to act in case there is a person in trouble in the water. Same as good samaritan laws, some cover you based on your "good intentions", according to other ones you must act. Be familiar with yours. (Also, don't forget to obtain consent before treating someone -EVEN when off duty).
I also remember watching on People & Arts once a show about a private company that cleans crime scenes after they are no longer part of an investigation (in order to provide a service to realtives and property owners). Anyways, the person that created it came up with the idea while working as an EMT and wondering who has to clean the mess... He bought a former ambulance (Ford E-350). He did leave the side lights but removed the light bar and painted it all plain / uniform white. [[JUST SOMETHING I REMEMBERED WHEN I READ THE THREAD]]
Well... Good luck and don't take unnecessary -legal- risks!
Saludos from Patagonia,
Guri