WHY would you have to change the box? Who told you that???
I have been using deep cycle type battery power to run my entire ham shack radios and emergency lights for over 20 years now, (With really good results)
I keep my deep cycle battery indoors inside a plastic marine type battery box.
(The big fear of so called "outgas" is not a problem UNLESS you had a commercial power failure and then try to recharge your battery rapidly. Under those conditions, Do provide plenty of ventilation.)
Do use a large size fuse right near the battery, Run nice heavy wire to your equipment.
I have found that a 10 amp FULLY AUTOMATIC battery charger is the best size to keep the battery fully charged with any normal transmit/receive duty cycle.
At around 50 bucks for a brand new marine type deep cycle battery, Less than 40 bucks for a 10 amp fully automatic charger, And around 5 bucks for the plastic battery box, You are still well under 100 dollars for a complete power supply that will also supply emergency power in the event of a commercial power outage! An AGM type battery is even better than the marine deep cycle type, But costs quite a bit more..........