Can rough roads create a suction from the water tank vent?

I too have this problem and here is what I thought might work but never followed up on actually installing them. Was thinking about some type of check valve in fill tube and vent. For vent line I thought this would workhttp://www.tibesti.com/shop/SHURflo-340-001-In-Line-Check-Valve/7UDQTY999Y and for the filler tube (big hose) http://thespaworks.com/parts/cal-spa-parts/valve-parts/cal-spa-2-inch-flapper-pvc-water-check-valve
But don't know if these products are designed to work from gravity for incoming water or actual water pressure against the flapper part of valve. Would these check valves solve the problem?
Then I thought about putting in plastic ball valves, but don't like idea of getting under the table and lifting up seat to open and close valves when filling each time and thought check valve would be better??????