Don't know about eastern Missouri, but in many of our state park and COE campgrounds, there is a semi-buried storm shelter, usually built of concrete block but steel reinforced, with reinforced concrete roof and storm resistant ventilation.
The bathrooms, if built of concrete block, could be reinforced, but there is no guarantee. If all brick (a construction used rarely here, brick is just a facing material) they don't really reinforce to 200+ mph.
In any case, a small masonry building is a better choice than being in a box that is going to be tumbling across the landscape until it breaks up. RVs are seldom much stronger than mobile homes, and mobile homes come apart all too frequently in thunderstorms, even without tornadoes.
Large masonry buildings, like churches, supermarkets, school gyms and auditoriums, on the other hand are very poor shelters. High winds lift off those large spans of roof, and once that enclosure is lost, so is much of the structural strength.
We have one church in town that has been hit twice by tornadoes, totally destroyed the first time, 1/3 of the building lost the second time. Since then, it has been damaged by straight winds in thunderstorms. They keep building it the same way, 20 foot unreinforced masonry walls, steep roof spanning the whole space supported only at the edges. If the wind moves that roof structure, it pulls the walls down. But it looks like they want their church to look.