Could be just terms just confused this simple mind, I too never heard camper mounts described as internal/external.
I assume referring to Happi Jack tiedown mounts, as they are mounted TO the bed, primarily inside as 'internal'-though the actual mount for camper tiedown point is external. Unless simply stake pocket tiedowns?
verses Torklift which are mounted to frame 'external'. Though either Happi Jack or Torklift mounts use an 'external' tiedown point. ie
Having had HappiJack bed/bumper mounts and currently Torklift frame mounts, the frame mounts, given the weight of our camper I believe a better investment.
Either system works.
H/J pros a bit less in cost, no additional hardware to install when loading camper, umm all I can think of.
Cons, cosmetically the little ears sticking out always bugged me. On our earlier design H/Js the 'ears' flexed bending my bed. The rear bumper button mounts totally useless on our truck, bumper material too thin, plus the attaching bent plates that connect to 'buttons that tiedowns connect to kept bending flat. And again silly bolts sticking out of bumper (now a permanent fixture).
Torklifts frame mounts opposite of above.
plus
A difference in the way truck handles was noticeable improvement, the amount camper moves inside bed considerably less. Again maybe truck/ camper specific but better angles for tiedowns IMO.
Cons: initial cost-likely higher install costs unless DYI. Receiver mounted arms do add a step in loading camper, (5 minuets to slide and pin) but I consider a positive, because when campers off-so are they- no 'ears'.