Maybe considering a Tunze Nano wavebox to replace my P/Hs. With the water in the tank oscillating back and forth, would this weaken the seams of the tank and/or the stand.
I wouldnt think so, I've never heard anything to support that. There is always water circulation going on in the tank, regardless of a wavemaker or not.
Constant oscillating pressure will weaken the tank over time. Your moving the silicone moreso than you would with a constant circulation. Should still last you about 3-5 years with a standard company built tank (AGA-perfecto) before you should consider changing the tank for a new one though. Evenness of the stand/tank and how big of a wave your running matters also. If your rocking your tank so that one side of the tank is half empty i wouldn;'t put the tank past a month =0P.
Be real cautious with what the stand is made of. I have mainly seen chipboard stands beeing sold commercially and thats not something you want to run a larger wave on. Your going to be seeing more pressure on the stand joints than you will on the walls of the glass once your dealing with a 700+ lb shift in weight thats sitting on the stand. IMO a metal stand or a really well built wooden stand is a must for the tunze wavebox type wavemakers.