I use two methods, one for small parts and the other for larger parts.
Small parts - Use Tamiya Clear acrylic. Also excellent for simulating guage glass on
instrument panels and dashboards. I always use this for wind screens
and clear head light covers on 1/43 cars.
Larger parts - Use G-S Hypo-Tube Cement , available from Micro-Mark. Also good for
attaching tiny PE and resin parts that need fussy alignment.
Both dry crystal clear and will never fog clear parts.
Pete