what did you guys use to attach the crossover inside the can for hlcds and how well has it worked?

Just use velcro tape. Works great

3M makes some serious double-side tape. I use it everyday on exterior applications.

Velcro Extreme, best stuff i've ever found and what is holding my crossovers for my MoMo's in the boat. Get it at Home Depot

Hot glue gun like the one you use for arts and crafts.

5 Minute epoxy or Metalset

spray foam just enoughf to hold it works great