What is the best way to freeze & reheat a quiche? I've tried it twice, and both times the bottom of the quiche became watery as it defrosted in the oven. I took the pre-baked quiche straight from the freezer to the hot oven. Note that both times I tried it, there were a few pieces missing from the quiche where most of the liquid collected. Also, I used a frozen ready made pie crust instead of one made by scratch.
I would use a pizza stone (preferred) or preheated baking sheet underneath the quiche, similar to the method sometimes used to make the bottom of pie crusts crisper. Put the stone or baking sheet in the cold oven and preheat the oven for at least 30 minutes before adding the quiche. This probably won't completely solve your problem, though. Unless the quiche is whole, I'm sure you'll still have weeping/leaking.
The water is likely from over-heating the eggs. They'll become rubber+water if you overheat them, just as badly as if you overcooked it the first time.
But quiche, pizza rustica, frittata, spanish tortilla, and similar are good at room temperature or just barely warmed through.
I would thaw it in the fridge overnight (24hrs would be better), so that when you're heating it, you don't have to thaw out the center. If you have something appropriately sized, you could thaw it in the fridge on a small wire rack (or maybe a few chopsticks) so that any moisture from condensation doesn't sit against the pie crust for long.
If you really want to warm it up, lspare's comment re: using a baking stone would likely help the crust, but it might overcook the filling. If you do it, I'd suggest preheating the stone, then turning the oven as low as it'll go 'til you get to the temperature you want.
There are a few other things that you can try when baking so that the pie will freeze and defrost better. First would be blind-baking the crust but before it's fully done, pulling the pie weights and brushing it with a beaten egg, then finish the baking. (to reduce moisture soaking into the crust). I've also seen recipes for other types of custard pies that called for adding a little bit of starch to the filling. (most recommend rice flour ... some starches don't work well if frozen or with milk).