I am looking for a practical way to prolong the life
of the wood frame in the raise beds I will start building
pretty soon.

The most practical way I know is to build your raised beds with
concrete blocks instead of wood.

If there's a place near you that manufactures them, you can get
"seconds" (which are not good enough to use in buildings but are just
fine for raised beds) for very little money.

Mine is two "courses" (blocks) high. The soil in it is about 1.5
blocks high. Very convenient. I can sit on the walls while I work on
the beds.

vince norris