You cannot mount a camper to only the Tacoma bed, but need to connect to the frame somehow. Searching on this forum will uncover folks who have made or have had made custom mounts, but most get the FWC brackets.
I don't think you would have to have the brackets installed by FWC, but you would need the tool that fits the bed bolt-head pattern. The brackets mount using four existing bolts which hold the bed to the frame. Eye-bolts then attach between the bracket and the underside of the camper. As I recall, the brackets were reasonably priced and you have the assurance of fit, good quality and strength. The current models also feature wedge shaped sub-brackets which help to center the camper in the bed.
edit: I've added a photo of my front mounting bar in a comment, below.
p.s., perhaps the party from whom you buy the used camper would sell you their brackets, too, if they are not going to install another camper.