battery deep cycle replacement

[SplashDancer]

Have a 2000 Dodge 3500 Okanagan with sealed battery box that is vented thru van sidewall. It will hardly or maybe just fit a group 27 deep cycle. Question is if there is a truly sealed battery alternative so I could install a larger , or 2 batteries for more capacity?

[SplashDancer]

Yes that was my question. Thanks for the response.

[Shearwater]

AGM batteries are truly sealed if that is what you are asking.