@Robert *********
I would not recommend this for a 4-months holiday . . . . the recommendation is, do NOT maximize the first 60 days out of a visa-exempt entry. Don't do the 30 days extension, save the 1900 Baht and the trip to Immigration . . . before the 60-days stay permit expires, exit Thailand to a neighbouring country, stay outside Thailand for a week or two. Then re-enter visa-exempt and get stamped in for another 60 days. This will GUARANTEE a trouble-free re-entry on a visa-exempt, since you did not maximize your previous stay - you look more like a "real" tourist and not somebody who wants to press a maximum stay out of touristic entries, which is heavily scrutinized by Immigration