Can I file a "storage" lien on a 40 ft. Camper?

There probably isn't a whole lot you can do as far as assessing fees for anything up to this point. You could try and sue them in small claims court but the first thing the judge is going to ask you for is a copy of the agreement you have with them that outlines the fee structure. Since you apparently don't have one the case would promptly be dismissed (it's all your word against theirs).

Send the RVs owner a certified letter telling them that they have 10 days to remove the RV from your property and that if it is still there after 10 days you will begin charging a (reasonable) fee for storage.

If they fail to remove it you can start billing them and if they refuse to pay THEN you can start the process of taking them to court. You need something in writing that shows that there is a fee expected and that they are/were aware of the fees and didn't pay them. Without that it's a MAJOR uphill battle.

We've called and left messages on their answering machine for the past 4 days and no reply. I've gone to the trouble to sit down and record dates and conversations since January, just in case. I cannot believe these people have done this to us. We did them a big favor because they were hauling a loaded trailer to Florida and couldn't take the camper with them and didn't want to forfeit it to the new owners of their property. If I had any inkling that this was gonna happen, I would have let it sit on their property and left the new property owners to deal with it. My husband is so pissed at me because I talked him into letting them do that...but that's another story.
Is there any truth in the phrase that "Possession is 9 tenths of the law"? lol

Is there any truth in the phrase that "Possession is 9 tenths of the law"? lol

There is in a round about way. You have control. If they wanted it back (how you wish) and you said "no" they have to go to the appropriate court to seek a judgement that this is the case.
I wonder if you towed in and left it in a public place with details of the owners set in clear view could be a solution. Is seems a way of getting out of the situation and pass the problem to the Local Government or appropriate authority. They have the facilities and resources to manage these problems and no doubt are presented with similar situations with abandoned cars. It may not be the best action but may see a happier result for you when the dust settles. Their refusal to take responsibility removes any moral considerations that you are not doing the right thing by them...at least in my mind.
alex

Well, my husband talked to the owners and he assured us (yet again) that the camper would be out of the driveway by the 1st of August. I sat down yesterday and wrote them a detailed letter of all our conversations and assured dates of removal and then told them that if the camper wasn't out of our driveway by noon on the first of August that a local towing company would be hauling it away (at their expense) to be stored (at their expense). The towing company said if they didn't get it out of storage in 30 days, the process would begin to get a salvage title, it would be appraised and then sold for appraised value minus storage and towing fees. The letter is going out as registered mail tomorrow.......TA DA!
Thanks everyone for your comments and giving me an extra boost to get nasty...shame it takes nasty these days!

Harmonyfarm--

Good luck. May your name be an omen.