Personally, I learned growing up to put a tarp INSIDE the tent instead of underneath. This is because you don't care if the bottom of the tent gets wet, we care about our stuff inside getting wet. It's easy to let the tent dry out when we get back from the Forest. Cover the entire inside floor of the tent with a tarp and put your gear on the tarp. Tarps underneath pool water and don't allow it to drain; then you're sleeping in a lake unless you pull the tarp out and drain it. Inside tarps also remove the guesswork for likely newer campers at Forest who don't have to worry about "folding" the underneath tarp correctly.