This is the way to do it/ cutting off of large sheets without a table saw.You make a guide with a piece of 1/2 x like 6" x 4'-6" with to screw to the piece you are gutting where your skill saw blade rips along the guide( be sure to take out for the thickness of the blade).You dont screw the guide screws all the way through..just enough to secure the guide to the board you are cutting( later you can fill with wood putty and sand down smooth later).Any Cheap Skill saw should work just fine..You can buy a cheap Ryobi with a laser guide now days with a storage case for under $50 bucks...But Buy a GOOD Blade..I use Diablo Blades and throw the blade that comes with the saw in the tool box for gutting fence post ect with that blade and use the Diablo Blade for good fine finish cuts..not the cheap blade that comes with the saw..that usually gets dull after about 4 cuts.Diablo blades are like $20-30 bucks, but last a very long time if taken care of and used right..Stored with a light coating of oil will keep from rusting and if you lightly wipe the blade after approx 6-10 cuts with oil it will stay sharp and not get dull and rip some nice cuts.A for the most part..Have respect for the tool, and use some protective eye glasses and maybe ear plugs,and go at a safe pace.Set the depth on the blade to penetrate like an 1/8" -1/4" past the depth you are cutting/thickness of the board.When you need to stop the saw to move to continue the cut.. move the blade back/saw back 1-2" then take your hand off the trigger and let the blade stop then move to where you need to finish across the board to finish the cut.Start back at that 1-2" where your blade isnt cutting anything along that guide, and then move forward to continue cutting.Just use a skill saw even if you have to set up a guide will still be better than having someone else do it for you most anybody with a little bit of wood working experience can cut straight enough with a skill saw to build a speaker box