James,

A Titan Viper is about as good as it gets pal, The only down side with them is the shape at the back, it means quite a bit of lost room inside the bivvy..
When i was carping, my preference was a bog standard Trakker Dillo, These have a flatter back section hense a much more useable area..

A mk2 version will give you a peak on the front.

Hope this helps pal.

Wideboy bedchairs will fit in the majority of bivvies nowadays. Even smaller bivvies such as the Nash Strongbow will take one with minimum of fuss. The new Titan will swallow one with no problems at all as the back has been raised up to give a bit more room at the back.
The Armos are also very good shelters and should take a wideboy sized bedchair with no problems.

Fishing long sessions depends on yourself. If the venue is one that you may need to up sticks & move to showing fish then a Titan might be a bit heavy if you don’t use a barrow.

The new Titan would be at the top of the list or very close to it, but the even NEWER Titan Brolly looks to be perfect in the weight/durability/strength departments.

ive not had good experiences with bivvys maybe because i go fishin by myself an find them hard to put up ive reverted to a tent myself haha. im selling a tfg xshell bivvy if you google it you can see it if interested give me a shout only used twice decent bivvy just cant do it by myself