Blocks are only as good as the person thats using the tool. Yes, find yourself a nice flat piece of oak. and cut em in any size you want. This will give you the flattest surface possible in the beginning stages. As mentioned above. I have used all sorts of home made blocks and barely ever had to buy anyones Hi dollar piece of foam. This works very well also in the cutting process in wetsanding your clear. Use the longest board possible for the panel your using. Method as mentioned is important as well. Without a doubt, use guide coat, I prefer the dust powder guide coat over the spray can ones. You want a panel flat, the harder the better. Be creative. Psa long board sandpaper on a roll can fit just about anything.