For boxcars, you might try removing the doors - usually a little easier although installing weight will be a little trickier.
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--- In STMFC@..., "Allen Cain" <allencain@...> wrote:
I have been buying RTR boxcars and covered hoppers for the early 1950s time period from Red Caboose, Branchline, Intermountain and Atlas and would like to add weight to meet the NMRA standards. Would appreciate advice on how to remove the roofs to get to the inside to apply the correct weight.
Hopefully this question is okay on this list as I do model the time period covered.