Creating decor

[Ryan & rosco]

Okay. A new 40 gallon breeder tank was just purchased for rosco as her 55 is getting to small because of only 12in width. Iv decided to make my own decor as far as my sandbox. The sand box will fill a little under half the cage and will be made out of 1x3. I will completely fill all screws and cracks with putty before the grout process. But what grouts and sealed and stuff like that should I use? I mostly have access to Home Depot. And lowes and a small do it best. Thankyou all for the help!