look at the FAQ

Residence laws for any EU country are the same, if you stay for longer than 3 months then you have to register Residence, which means that is your permanent/primary home.
For Portugal the Portuguese Tax office would consider you to be a tax resident if you own a home here at 31st Dec that they consider to be your primary residence whether you here 183 days cumulatively or not.

In the FAQ this site clearly states they cannot be used for a permanent tax address which as a Resident you would reguire.

If you don't intend to be a Resident or visit for more than 183 days cumulatively in any 12 month period then it isn't a problem.

So for anyone considering a mobile home it's not only the legality of park to check but also any statements like the one I quoted.