I thought long and hard about installing an under the frame water tank. It would lover the CG, and be out of the way, thus very conveniant. I would not have mind at all to fab it. The two factors that brought my tank inside the front was:
1: Protection from ground strikes. This trailer is extremely capable to go literally anywhere, and as I fabbed the rear bumper, I was concerned about the jack striking the ground, so I made them so they can turn horrizontal in case you have to forge crazy up and overs. I felt by putting a tank under I would deminish the capability of the unit. Now I, off course, never took the trailer to that potential, but I could have.
2: Cold temp impacts. I do camp and have in the past down to 19 deg F with winds at 60 mph. Yep, I got caught at 10600 feet, but never the less, all water was frozen. There was a foot of snow and ice pelets next morning, and the little generator was running at 15% chugging along to deliver power to my 200 watt ceramic heater in the tent. Gen was about covered with snow but running and exhaust was clear. I did have a 5 gallon water tank in the back of the car and that was not frozen. At that point I determined that if I did a tank install, it had to be enclosed and protected from any of the elements.
I fully understand that this may not happen to anyone and dont at all mean to pick on the design under the belly at all, I just wanted to share what went into my design and thoughts. I did also consider just to pay an aluminum fabricator to build me a box of the same design I ended up with but in aluminium. I reconed that about a grand as in Colorado is very expensive, and the composite box cam in less than that in materials. I simply cannot say enough about the convenience and practicality of having a big roomy box up front. IMHO this is what the aftermarket guys should be offering as a second. The first is the rear tire swing carrier. Once that spare is out of the way, then an aluminum box. Then you can customize it just as you would like.
Now back to the regular scheduled program....
Cheers.