I went the difficult route. On my YZ I took 1" tubing and 5/8 round stock center drill the round stock for inside threads, drill 5/8 holes in the 1" tubing weld the drilled round stock inside the holes you just drilled in tubing and then weld the tubing to the bottom cradle of your frame like crossmembers. I formed 1/4 aluminum to fit the cradle drilled and countersunk the holes to bolt up to the crossmembers.no welding of the aluminum but plenty of steel welding.
On my project dual purpose wr I took that 5/8 round stock center drilled for threads, drilled 5/8 holes in the frame and welded them into the frame much like the motor mount bosses in the front. Did the crossmember deal in the rear. Form your plate to the cradle, make ears that will bolt to the bosses and weld to the plate. If my plans work out the way I hope my skid plate will double as my battery mount and as a center stand.
My skid plates are overkill ,not for the faint of heart to fabricate,and you must have absolute trust in your welding capabilities.
I have seen Rm guys skidplates very nice, effective, inexpensive,and simple to make. Looked like he didn't have to take anything off of the bike just measure , fabricate, and bolt up,very clean set up. If I didn't enjoy spending the time in the shop as much as the trails I would of definately done it his way.