Cleft is best on the new sprouts. Veneer can be a challenge due to how soft the wood is. Use fully hardened scions (not tender red-stage ones). Tender scions die too quickly. Fully hardened scions can last longer (to wait for cambium growth).
No need for a greenhouse. However, if you want to increase your chances of a take, you can leave 2 leaves on the scion, cut such that only about 1/3 of each leaf remains, and wrap the entire 1 gallon container in a plastic bag. Keep in the shade until scion starts to grow, then remove bag and move to sunny area.
Nonetheless, just a typical cleft graft (with no leaves on the scion) should give you 50% take or better.