Water tank question

Winterizing is technically only necessary when you need to leave the van outside for awhile without heat in the winter. While you may not plan on having that happen ever, I would very strongly suggest at least allowing for the possibility of winterizing somehow or another; things can come up, and having that available could be a big relief. Note that you don't need to have the valving and suction inlet at the pump to be able to winterize, at least in many cases. A carefully placed low-point drain (so you can run the pump dry) allows most of the water to be drained by gravity, and then you can either pump in antifreeze via the city water pressure connection with, for example, a hand pump, or else blow it out with compressed air at a moderate pressure. In a pinch, it's also possible to drain the fresh water tank, dump in a few gallons of antifreeze via the gravity fill port, and then pump it through the plumbing...that method just takes a comparatively large amount of RV antifreeze.

In theory, it could also be possible to completely drain all the plumbing purely by gravity with low point drains, but that's often more practical in houses (where level doesn't really change) than in vehicles (where the angle of things is liable to vary depending on where you park).

RV water pumps do generally have a check valve built into them. If, by some strange design, your pump does not, you can insert a separate one on the suction side of the line. Assuming it's an on-demand pump, though, it pretty much requires a check valve to operate properly (as otherwise it would never shut off for very long as the pressure would leak back through the pump).