This post involves two subjects. This month is DE, PA, NJ, MD, Model Railroad Open House 2021 in our area and the inspiration is outrageously fantastic!!
Our RR is at the limit of construction in our basement.
Some of the local RRers having also reached the same point are on the open house schedule this year. I have visited some RRs of these folks to which I have not been for a while. These guys, having also reached their maximum building footprint ADDED ON to their basic structure. What a difference it makes all the way around.
If you want to see these improvements check out the schedule. It can be an easy sell because the added basements also present the benefit of added master bedrooms, sewing rooms, and other rooms which spouses like.
One of the guys who shall remain nameless sold his spouse to putting on a kitchen addition never getting into details about the depth of the foundation or ease of connecting the additional basement.
Think out side of the box.
The basement is just the required foundation, why in the world did you feel the need to mention trains. 
