sounds similar to our '04 - ours has the same motor (pre-emissions, no egr cooler) but ours has the ZF / Meritor 12 speed auto.
1st time ive heard of having TWO heaters.
your gen is same size (10kw) - which will be PLENTY (expect at 1/2 a gallon per hour consumption).
youre gonna LOVE that outside cooler (no ice to buy)...I added one to ours and we use the hell outta i.
your tanks are similar size except we have 220 gallons of fresh water (twin 110s under the queen bed).
'04 Haulmark (M42386) 42', 2 slide, 10kw - Pictures
'04 F350 CrewCab Longbed 4x4, 50g aux tank & gear vendors dbl over