Welcome to APUG.

Which type of tanks do you have? The caps vary between the versions. You may want to post a photo.

Rubber bands or an empty reel work well instead of the clips. In fact, an empty reel is probably the best.

Don't use the rotary agitators. If you must avoid inversion, just move the entire tank in an exaggerated figure eight.

By "auto-load rollers" I expect you mean reels. In addition to the Paterson versions, there are generic versions (AP, Samigon, Arista et all) with wider flanges that work as well, and some prefer.

Have fun!