If a tanks not baffled properly the liquid is not stable I wouldn’t think a frame would help much Daz,my tank is properly baffled I have one of Neils,tbh the safest tanks are the ones he does that are built to go round the wheel arches that are flat.
It all depends what sort of driving you are doing if you potter round town or hardly leave a village I wouldn’t be worried,it’s when you are motorway driving or doing those sorts of speeds I’d be more concerned.