3108 + 742 = 3850 GVWR? Seems about right for a small single axle trailer. That is a huge fresh water tank for a tiny camper. So your conclusion seems about right, 52 gal x 8.3 lb/gal = 431 lbs.
My parent's little single axle camper, Funfinder X 139, has a GVRW around 3800 lbs if memory serves, seems standard for a single axle. Tanks are more like 20 gal fresh, 10-15 gal gray (it always fills and backs up in shower), I'm not sure of the black tank capacity. Thankfully never backed up!
2012 Aspen Trail 2710BH | 280 watts of solar on the roof | 2x6V GC batteries | 100% LED lighting | 1500 & 300 watt PSW inverters | so far strictly boondocking