You mentioned you have a garage. If you're willing to sacrifice garage space for the railroad, you're on your way.
If you're still looking for larger, wide open outdoor space maybe you can make a deal for someone else's property. I've done this kind of shopping for space for a local train group. It's not easy, if you basically want it for free. Patience can be rewarded. It's a like like kissing frogs. It's unpleasant to start, but great when you find a prince. They're out there, so it's worth looking.
Personally, I wouldn't give away my equipment, buildings, track, or plants, if I'm already providing my time for free. Usually, the property owner wouldn't know what to do with them anyway.
I strongly suggest that you get a signed agreement that makes certain things crystal clear. More than one club has been badly burned when their space changed owners or life happened. A lease can make ALL the difference. It can be a simple two page agreement that says what you agreed to in plain words (that can't be twisted later), or as complex as you wish.
I'll start the ball rolling below.
It sounds a little formal and harsh, but it can save you when you need it most.[I've seen the anguish not having a written agreement has caused grown men after working on a model railroad for years.] Think in terms of your worst enemy kicking you when you are down. When writing the contract, "hope for the best, prepare for the worst". Leave no wiggle room.
Actually, property owners are rarely your enemy. They just think you're a little crazy and want to sell their property or expand the parking lot or building. Trains are OK, until things change. Usually, they just don't get trains and have a totally different agenda.[ Make sure the lease is binding on the current owner, its agents (owner's puppets), successors (the next guy), lenders (if he goes broke), and assigns (also the next guy).]
You might even want to put it in the form of a ground lease that says they give you permission to enter into the property at any time and occupy and use it for the purpose of preparing and operating a model railroad display, and activities related to that. Specifically mention access to electricity, bathrooms, storage, parking, pesticides, drainage, and possible plantings or changes in the soil. The lease could be in exchange for some small fee such as $12 dollars per year for 10 years, payable annually.[This is a bargain price for space, but it's real too. All deals relating to real estate must be in writing to be legally enforceable.] [Make sure to send a good check with the memo part filled in, certified mail return receipt requested. Keep the cashed checks and signed C.R.R. cards to maintain a record of payments.] You could also open the layout two times a year for display for their employees, members, or public as they choose. Make clear it would be opened on dates and such time as you will set in consultation with them. [Also make clear the rest of the time is yours and they do NOT have the right to have visitors come in.] They may waive having an open display date at their option and shall give you 30 days written notice in advance if they plan to do so. [So they can't blame you and break the lease] [Add any such letter to your permanent file.] The display will be "As Is", "Where is", and reflect the current state of work based on your own schedule and designs. [The "don't rush me, this is a hobby" clause.] The layout may be changed from time to time in your sole discretion. [The "I'm an artist" clause.] [Take dated photos of visitors and add them to your files.] Make sure Lease is automatically renewable and extendable at the same rate and terms for two more 10 year periods. [Or some other agreeable automatic renewals.] [Yes, thirty years. You'd be amazed what how long these things can go on. One club in our area regretted not making their deal even longer.] All equipment, track, and other improvements are and will always remain your property. At the end of the lease you will remove your track, buildings, equipment, and plants, but not the gravel or soil. You will have your own equipment insurance for fire, theft, and vandalism. They will provide liability insurance for you and all visitors. Throughout the lease they will provide security and lighting equal to the rest of the public areas of their facility. In the event of a dispute the dispute shall go to American Arbitration Association arbitrator according to their rules, and the result will be binding and enforceable in local court. (This could save months and months of delays in some some Court calendars.)
This will show the property owner that you are serious about this relationship and most business-people would rather know what to expect than wonder if there's going to be a bunch of disagreements later.
It all sounds a little scarey, but can work out very well. And you can have years of fun!

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