Possible Clues:

• Initially too puny to be like country gentry
• Temperature's weak of the upper crust
• Like Miss Marple's attire
• Like some professorial wear
• Robust and rural (of gentry?); wet dye (anag.)
• Like well-off people in the countryside with an interest in horses, dogs etc?
• Outdoorsy leader of trek, thin
• Collegiately stylish
• Posh, outdoor character's introduction of tree, as garden overlooked?
• Yen to be by river, like upper-class countryfolk?