We purchased an '86 BA700 this year which was in fantastic shape.  We have
used it quite a bit this year with zero problems.  Very little has been
changed from original as far as I can tell and everything is in great shape.
No tears or holes in canvas.  It has been through a couple of very rainy
weekends with no problems.  The previous owners replaced or added (not sure)
a brand new fridge and water pump.  We have not used the water pump (no
need) and have only used the fridge once as we usually don't camp at sites
with utilities.

I would like to update the interior... mattresses, curtains etc

It's a great little popup!

Cheers!

I still have a 1976 BA700, but it has not been on the road for some time
now.
It was our first pop-up, purchased used in 1986 for $2000 CDN.
It weighs about 900 lb and towed remarkably well with a Taurus wagon at
120 kph.
I replaced the canvas in 1990. The only problems I had were the manual
water pump, a heater element on the Dometic fridge, one wheel bearing
failure and one tire delamination. We went every summer from Montreal to
either Virginia Beach or Orlando with it. As the kids grew the Bonair
became very small - 7 foot box.
We upgraded to a Coleman Westlake with A/C in 1999. The Bonair remains at
our country place where the friends and family camp out on the property.
It was a good trailer, we probably towed it over 30,000 miles.  My only
dislikes were the troublesome two-piece door and the very thin (1-1/2
inch?) foam mattresses. Also, the ground wires on the tail lights caused
intermittent problems and needed to be cleaned/checked each spring.