It sounds like your father would be comfortable with the size and form factor of a mod, which is good. They are much better constructed of heavier aluminum or stainless steel, when compared to the disposable eGos. They'll be able to take some physical abuse and keep on working.
Whatever mod he should decide on, I would recommend a
belt holster from
SerenityGear Leather if he plans on keeping it on him at work.
For mods that are extremely durable and in the intermediate price range between a Bolt and a Provari, I'll recommend either the
Altsmoke BB or Silver Bullet. Both are $85. Both are made from heavy aircraft-grade aluminum that could withstand being driven over by a car or truck. High-use rated quality power switches. Silky-smooth, well-machined threading. USA-made with the customer service that only American companies can provide, even after warranty. I have both and love them both for different reasons.
The BB is smaller and lighter, so therefore more portable. The Silver Bullet is larger and heavier, not especially pocket worthy due to its size unless you have big pockets. Both hit equally well. Although I don't own them, also consider the
Alpha and Omega mods Altsmoke offers. I wouldn't necessarily go with their starter kits but would buy only what you know your father will need.
AltSmoke.com | Personal Vaporizers | Electronic Cigarette | Ecigs | Electronic Cigarette Starter Kits | The Yeti, Joye eGo, eGo Dual Coil Cartomizer, Silver Bullet, BB, Omega, Alpha
I don't particularly like metal tanks, but in this situation it might be a better solution. Maybe something like a
anodized aluminum or stainless steel window tank from Big Daddy Vapor. A little pricey at $48, but you probably wouldn't find a tougher made tank considering your father's work conditions.
Big Daddy 5ml Tanks & Tubes : Big Daddy Vapor
The pyrex tanks from
Phiniac Rugged Pyrex Glass Tanks are probably durable enough and in the same price ball park as the Big Daddy tanks.
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BB and SB size comparison / BB / Silver Bullet