prime focus dish is one that is setup like your 12 ft big dish
so it should work. , there are or should be cheap versions out there that would work with your dish.
here is one listed at one of out sponsors
problem you will have is adapting a scaler or holder for one of these prime focus lnbf's to your dish. unless it will fit into the scaler you have. another option is to take the scaler you have and buy one of those listed above ( or anyof them with a scaler) and going to a maching shop and welding some holders onto it so it will fit the scaler arms. or making new arms that will fit.
if it was me and i decided not to go the bcs-621 (and widen the scaler a bit ) or go the corotor route. there is something you can do but its more experimenting. you can offset a cheap prime focus lnbf from the main lnbf (tee-comm). several people have done it, but it will take alot of tweaking to get it placed just right. i have a dss lnb on my 7 1/2 fter but signal is low -mid 60's cause it is a offset lnbf. The BSC-621 or the corotor would be easier.
for wind problems , low to the ground is best.... if thats not possible maybe a windbreak