Naturally the busybox utilities do not have all the command line options that their heavyweight counterparts have so makepkg has option problems with id, du, tar, and find. You probably don't want the "du" change but its here for completeness.

Fixes:
-for id no "-u" in bb so use $UID instead.
-for du no "-b", report pkg size in K
-for tar no "--use-compress-program", use -j and -z
-for find no "-not", rework with while loop, if, and grep.