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Both options would work fine and may even be a bit overkill. A 4" thick pad is definitely sufficient. Hell, you can even just do a crushed rock base and build a wood perimeter to keep the gravel from washing out. I recommend using 3/4" to 1" sized rock. Smaller stuff like pea-gravel doesn't work as well and it's more viscous.Grats on the purchase by the way. I really like that new model and can't wait to get one for our showroom.