MadDog - Regarding packs, I don’t suspect you’ll find a pack to rent for 6 weeks. I think that idea is designed for a 2-3 night trip. After 6 weeks, you’ll likely pay more for the rental than your own pack. So, I fear it’s time to take the financial plunge.
When looking for a thru-pack, look for something in the 3500 cubic inch range (less if you trim gear down to the necessities, more if you add some extra creature comforts). And keep the weight of the pack in the 3-pound or less category. Some packs can get needlessly heavy, quick!
Some good bells and whistles to look for are a lot of external pockets for quick access to gear needed thoughout the day, hip belt pockets (same reason), water bottle pouches you can reach while the pack is on, and frankly, given that you’ll be hiking in Colorado in the fall, I’d pick a red or orange colored pack to provide a little extra insurance against over-zealous hunters. Avoid any pack that boasts a hip belt or shoulder strap system that looks more padded than a recliner chair. The plush accoutrements are most likely needed to mitigate against the pack’s own knee buckling weight (when empty!).
ULA Equipment (Circuit and Conduit) and Go Lite (Jam) make packs that have served me very well over the years. I’m not a fan of Osprey, but many fellow thru-hikers swear by them. Give them all a look.
Matt