I dont do a lot of outdoor stuff so someone else may give better advice.
I would go for a pure oil put on hot to increase the absorbtion.
linseed is cheapest but if you check out some of the other threads on this finishing forum, youll find heaps of info and opinion.
youll have longer drying time with a pure oil but the upside is you can recoat straight on top when it looks a bit tired.
your energy and focus in this heat is amazing:U
Astrid:)