The area around Peniche is popular for holidays, similar to some other areas along the coast, most of the accommodation is aimed at short term holiday lets within the " season". Also a 6 month let is too long for holiday let but short for a "permanent" residential let. I'd suggest you book something further inland for a few weeks then investigate the areas you wish to live and then visit the local estate agents in person. For longer term/residential lets it's usual to view the property before agreeing and local estate agents may not take you seriously is it's only done via the interwebs. I think (just an opinion) some agents have wasted time and effort on accommodation enquirers from outside Portugal which do not lead to them being paid and are a bit more circumspect. You'll probably find a NIF (tax code) and Portuguese bank account would help in a residential rental but these are easily sorted (with a non Portuguese address) when you are here. The guarantor/six months up front will vary from agent to agent but basically they are trying to ensure the rent is paid by a non-resident who can just leave and go to a different country.

 

I wrote an article about our experience which may be of some use Portugal Long Term Rentals Challenge - Roving Retirement