I used normal masking tape. Blue painters tape to be exact with a 2 inch width. Just be sure to peel it up when its all still soft but hard enough to where you won't pull up the liner.
I had no issues what so ever. Professional applicators use that because their stuff is thick and needs that kinda tape.
Also, if you are using the DIY bedliner (Herculiner,Monstaliner, Raptor) Ive noticed they dont get as thick as the Professional kind. They work just the same but are not as thick. you can go thicker but adding more coats onto it, but thats going to be a while. To match there thickness, im thinking anywhere from 6-7 coats of herculiner. Thats APPLY-Wait till tacky-APPLY-Wait till tacky and so on and so forth.
Hope it helps.