Question about Practice/OTAs/TC/etc (Indoors vs Outdoors)

[DoobieKeebler]

So, I'm watching Hard Knocks and thinking about how miserable it must be to practice in that sweltering Georgia heat (something HK referenced last week). That got me to wondering, are there any teams that normally practice or run their off season programs indoors?

If not, I wonder why not? The only reasons I can think of would be
1) Some team HQs/Training facilities are not next to the stadium.
2) Wanting players to acclimate to exerting their bodies in extreme heat.
3) Stadiums are used for other purposes during the week, like concerts or monster truck shows. (Graaaaave Diggerrrrrrr)

But even with the examples I listed above, I'd imagine coaches would want their players to be practicing on the same surface (grass/turf) that they will be playing on during every home game.