I just pinch the line and spin the filter on dry. I don't see any reason to pre fill it. I don't think the little bit or air would be any issue. It would get air in it when you change the coolant out also. Not sure why people keep writing that the coolant filters don't filter anything. The ADDITVE CANISTERS do not filter, just slowly release additives. A coolant filter is just that, a filter. The one I listed is a 40 micron to be exact. I think your idea will work and be easy to get to. Definetly be more difficult on your coach to put it in the back because there is no factory provision for the coolant filter. If you have a motoraid water heater system on your coach you could use that line also. At 2 gallons per minute theoretically all of the coolant in my system is filtered in 6 minutes. Now I think it would be a lot longer because not all the coolant is going directly through the filter, most will bypass it but will eventually get through the filter.
07 Winnebago Vectra 40 TD ISL 400. Tru-balance, centramatics, Koni shocks