Why? Your chassis battery should only be used for starting, with the alternator providing the running power and charging.  The fridge, radio, interior lights, and cigarette lighter should be hooked to your isolated second "coach" battery.  The chassis battery is adequate for starting. The box is vented and in the wheel well, best left alone IMHO.

If you want to fool around do this mod instead: http://peacevansseattle.com/specialty-mods/ 

Stuart

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Neil2
Sent: Tuesday, February 07, 2017 1:47 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Modification, Battery box, bottom

Hey volks,

I'm considering a new engine battery and wondered what the experiences are and pros/cons of cutting the bottom out and extending it an 1"~2" for to accommodate a mo betta battery?

Please/thanks!

--
Neil2
'82 Diesel Westfalia (Ducky)
'86 Vanagon (SaVannah)
'08 170" 2500 Mega Roof Sprinter (Moby)
'90 Westfalia Subagon (SaL)
Fulltiming since August 2008
Nunquam Pendite Divendium