Trump would never be anyone’s VP even if they wanted him, but I can envision Trump picking Cruz as his running mate, if he were to get the nomination.
Trump might surprise you on the issue of VP. If he is serious about saving the country for his grandkids, he might take that VP slot with a candidate he respects. He and Cruz are in agreement on the issues.
Cruz would want his VP to be a vital part of his administration. I think he would turn Trump loose on negotiating with foreign countries on trade and policy.