I like to do the vendor liens as this gives me an additional monthly income and the possibility of the purchaser to default and I can reclaim and resell. 

I've seen some listings use a composting toilet and reclaimed rainwater filtration system for applications in mobile "tiny houses", which sounds like what you're going for.  

You'd have to be sure there were no deed restrictions and you'd need ot be aware of the reclaimation period in your area but...you could buy a mobile home like the one you mention in your deal and move it to the vacant lot.Again, in Texas, you can acquire a lot for a couple thousand - a mobile home for the same - and pay to have it moved - you'd be in the deal for $5 or $6k and could then rent it out until the reclaimation period was over.

The liens never attach to you personally; they instead are linked with the property in an attempt to reclaim any of the debt when the property is sold.  

vs. if the owner is alive and you just have to worry that they were properly served in order for them to try and reclaim the property?

They may be slightly different with housing authority involved, but it shouldn’t be hard to reclaim your property.

The Bad: If it is a Tax Sale Auction, you may not be able to get title insurance on the property for at least 1 year; this is due to the city reclaiming many tax delinquent properties without due process to the previous owner.

I utilize a lot of reclaimed wood, plus steel, iron, copper, and aircraft cables. 

Also, I read somewhere that they may have a right to reclaim their title??

"No hard feelings, I don't want you to have to pay me late fees - but I must reclaim my time." etc.