Can't decide whether you want a fully enclosed ARC or one with a pegboard on the side? 

Why not have both! 

I modified thrutheframes ARC-PEGLAGO panels slightly so that they can be printed in 4 parts on the P1P.
You will need to print 8 parts in total.
Four of thos are need for the "airtight" inner pannel and four make up the pegboard.
The inner once are mounted to the sandart ARC enclosure with 6mm M3 bolts.
The outer pannels are mounted to the inner pannels witch 20mm M3 throughbolts, nuts and washers.
Ther is enoght clearence betwen the pannels and the printer head assambly.

This is not a perfect "on-stopp" sollution and ther is definetly some room for improvment.
Never the less this resault works for me.

The .stl models need to be ungrouped and divided on to four printing plates.
Expect around 20h of print time. 
Supports are needed.
~600g of filament are needed.