@Eric F. , I would determine that based on the total amount you spent prior to getting the mobile home rented. The less the MH cost you to purchase and fix up, the better that $300 will feel each month (your capitalization rate, which is the ratio between the net operating income produced by an asset and its capital cost, and actually does not count the purchase price of the asset). In the example below, I counted the cost of the purchase price of the MH asset.
For example, if you purchased the MH for $2000 cash and put in another $3000 cash in repairs, and all of this is completed before your first lot rent bill, your total outlay is $5000, without any financing. If you can clear an actual $300, after all expenses, for a solid 11 months (factoring in vacancy), that makes your cap rate 66% during that time [(300 x 11) / 5000 = .66]. That is DARN good!
Insurance for my 1982 MH is $25 per month and I have also added another $25 - $30 per month as a maintenance factor....the "just in case" clause. One more item is vacancy, as it is difficult to keep them rented during a tenant transition. With all of this, do you still have a true $300 each month?
So, now to answer your actual question "should I be able to cash flow in the long run or is this too thin?", I personally feel you can. The MH is a cash-flow machine, like a washing machine at a laundromat, and it depreciates like one as well. Therefore, keeping them rented is very important in your cash-flow game, as they will not go up in value like a stick home. If I could ever figure out the SAFE Act correctly, selling them on contract is a way to capture some "eye-of-beholder" appreciation...but for now I will just rent them out!
Best of luck and please let me know how it goes with this MH.