I have yet to have that happen in the 6 years I've owned my van but I do have solar. Maybe you should do a check on the battery system just to make sure. If the van has a separator, it should have protected the starting system. But there are other items that are connected directly to the starting battery system that could cause you to kill your starting system. On my van, one stereo amp pulls off the chassis batteries. Dome lights and front 12v outlets also pull off those as well. I had a separator fail on a trip to Colorado years back that caused me some trouble but I still was able to make it through the trip. I'm wondering if you have a bad starting battery and the house battery system is masking the problem by assisting the starting of the van... it's just one thing you should look at. Lots of info in the FAQ's viewtopic.php?f=14&t=2167
A generator can be a nice backup but I decided one wasn't worth the space it takes up for my needs. If you have a starting battery fail out in the field, more than likely you'll have to address the battery problem and a generator won't help. Still they can pull you out of the fire at times and if you do want one, the gas versions manufactured these days are so well made I wouldn't think about a diesel generator. All you might need is a small external fuel tank like those made by Rotopax
I'd like to hear from sombody using one of these:
Hopefully something like those will be more cost effective in the future.