I have a wool half pad that has memory foam inserts for the front and back.

I am considering trying to use this pad with a trial saddle to see if I can get it fitting right.

Question, the inserts are supposed to be memory foam, do I just pop them in and put the saddle on?
Do the inserts hold their shape, do they take a while to mold to the correct shape?
Are they still flexible and giving when molded? (they just seem so hard to me)

Ideally I want a saddle that fits correctly without inserts but until I find that saddle I am considering this route, so any tips from your experience will be appreciated.

There is the possibility that even with the inserts the saddle may not be right but since it is quite close I am hopeful.

Do inserts tend to make the saddle slip more easily?
I know inserts can be great for a transition from not fit to fit but how long would you consider using inserts, as a permanent solution?

Also, this is for a jumping saddle and would only be used once a week and for clinics. (just starting jumping this horse so jumps are lowish)