Birch wood is the preferred . Hobby lobby or your LHS have what you need. Epoxy in .
Zippkits has Balsa angle stock used inside the radio box corners and flats ,Shoe goo or silicone all back hardware screws before you head to the water or that radio box will leak. The balsa is light but strong when used with CA and 30 min epoxy. A easy light helpful water seal out.