Unless boat is assembled full time adding an A frame to your kit is going to be a right palaver and might make you use the boat less. Going on the principle of something easy gets used the most..
I’ve heard of others using plumbing waste pipe which could be dismantled to make a portable A frame. Most use diagonally mounted(to the inside of the transom) slotted 1 1/2” ~ 2” plastic waste pipe to hold a couple of rods. Tackle shops/boat shops sell dedicated rod holders that can be clamped to a seat or transom top.
Have a search on this forum you’ll find a few ideas and photos.