If you need a DC DC you might consider a Vicor MegaPac. It can give you a stable voltage output for your accessory systems and even custom outputs for other items you need to power. If you need only a small DC DC you can use bare modules with a heat sink and put power to them if needed and they are sealed. The MegaPac is not water proof but if you keep the top on and keep it from getting wet in wet weather you should have no troubles.
As for disruptive technology I can say with out a doubt that electric cars are not disruptive but the batteries being used in electric cars are. As such the electric car can be built and sold successfully by the current auto manufacturers. It will take visionary people to move the movement forward but this is NOT the same as the internet of days gone by. In the days of the early internet it was a disruptive technology and no one on earth had the internet. It WAS totally new and disruptive. Cars are no longer disruptive. The batteries that make them viable are disruptive only because they can be used now to power a car and makes gasoline powered cars obsolete. That is the disruption.
Nissan has done a bang up job with the Leaf and I can assure you that the Leaf is NOT a converted Versa. Not even close. The only thing in common with the Leaf is some vague looks. Very vague looks at that.
We do need to get the electric car in the public eye and that is why we should not build total junk. It is possible to build a respectable electric conversion with out breaking the bank but it still won't be cheap. Fiberglass bodies are kinda cool but most are only open top roadster types or just too damn small for the average person and not really suitable for a daily driver. Converting a clean car is fine as long as you like it. Don't just do any thing you may have. Most of those are pretty lame and present a poor public presentation. Not what is wanted.
The auto manufacturers will do a fine job as they can hire all that is needed to put together a system that can be done in house. Like Jack says, vertical integration. Nissan is doing that. Nissan has a visionary but not like we might expect. It is amazing that we think all visionary people are like Musk or Jobs. Hardly. They are and were great but there are others.
Hot rod types will latch on but in limited amounts. Not much you can do to make a motor pretty. Even the pretty ones I have seen done are hidden from view mostly and that is not what hot rodding is about. Hot rodding is about showing off. It is an art form. I don't see it as a major player. A player yes, just not a major one.
The move to electric cars will NOT be the same as it was with the internet. The disruption is not as grand. Now if we all rode bicycles and there was no such thing as a car then I could see a car being a disruptive change. But since cars are so common and electric vehicle have been around for quite some time in some form or another I do not see it as being terrible disruptive. It's only because of the battery and yes the auto manufacturer will be able to innovate new designs and build them. They do it all the time. A few players will emerge and play in the game. Most playing will be in the battery and instrumentation. Motors and controllers are available and once other car manufacturers see Nissan doing there own motors and controllers and batteries they will follow suit.