Box section end caps

[gaz1]

sorry for bringing an old post back up

i need some advise and as this tallys in with what i am after i thought id use it

now what i am needing is where the metal joins together against the other metal but it needs to be taken apart and reassembled often depending on usage

now i understand theres welding a nut inside the metal 25mm x 25mm box section and there is a nut and bolt place near by
or theres using a barrel nut just drill through both steels and connect up

then theres a threaded insert plastic metal nut there is a drough drawing of what im after the green lines are the bolts

so may i ask which is the best to use for a novice welder as im already half way through that frame build already