I'm in the double check on WDH as well and it will add tongue weight.
Also know that you can't load your van down to the gills too when towing. I love stow and go and fold flat seats but you need to watch weight, especially in the back.
I wouldn't tow with full water tanks but I dont' think that's a problem with a PUP. You don't have a bathroom anyway. We camped in a PUP for 8 years and never filled water and I had a truck that could handle the weight.
Head over the PUP forum! Not that active but lots of good info.
