Not normally you don't, you don't need anywhere near that unless you've got a MASSIVE battery bank.
20/30A split charge relays are the norm, and fine for around 200AH habitation. Virtually all "standard" pro conversions will be to this scale.
The ctek d250s system we are putting in electronically only pulls 20A from vehicle but has an option to pull more, but we won't want/need it. We have 2x 100AH batteries.
You *can* use a 30A standard split charge relay to pull in a heavy duty relay, but generally not needed <200A. This is talked about a lot but seriously not needed.
You can get a voltage sensitive 140A relay for c. £30-35 on ebay, but I don't like them as its possible to tick on/off/on/off if batteries a bit flat. Also, if you are considering >>50A - the cabling and fusing us rather big and, in my view, puts too much strain on engine.
My last van had 30A split charge relay (smartcomm cheap thing) with 25A fuse - 200AH batteries - and we wild camped for most of the time and it charged fine.
Each to their own, but look at maybe the VW forums and ask there - its unlikely any of them go large.