We have already found ourselves in situations, in Colorado of all places, where we needed to leave an area due to safety concerns and having cab access to drive away is important to us. Are we being overly paranoid on safety issues, or is this a legit concern for international travel?
I have the same camper so can address some concerns. I think the volume of inernational travellers would suggest that this is primarily a non-issue. It's something that comes up a lot in conversation. The camper is high off the ground and we pull the stairs up at night as a precaution and they hide away nicely. So, safer than most camper in that regard. But through the pan-am we never had any issues. Also, if the person is seriously posing a threat then it's not like they can not block the truck or break a window. There are limited situations where having cab access would be genuinely beneficial. I get the concept. But in the real world it's unlikely and probably way less his than driving the truck on latin American roads anyway! Having done it, it's not something I would bother accounting for and would not be on my shopping list as an essential. We have camped the street in Bogota (got woken up by a man knocking on the door with two coffees saying "Welcome to Bogota"), we camped in town plazas all over Latin America, side streets as well as the usual more remote camp spots. Never had an issue. The country we felt least safe in was the US and we didn't't feel particularly unsafe there.
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As for the pop top, safety and weather come into play here. Gone are the days of sleeping in a RTT with the whap whap whap from the wind or rainstorm. How does this hold up in those kind of situations?
Very well. The material is thick, multi-layered and quite taught, not very tall and held by a solid edge all the way along the top and bottom so there is not much to flap. There is some movement in hard wind conditions but it's a country mile away from being a tent scenario. The camper heater is also wildly over spec'd for the size of the camper. Heat is not an issue even in the colder climates. There are Nimbl owners who use their vehicle for snow sports so .... there's that. Generally, the pros outweigh the cons. Dropping all the windows and waking up with a 270º view in a great camp spot is hugely entertaining. You don't get that with anything else.
My biggest issue with the Nimbl is the inability to simply get out of the truck and open the door to get something. We plan a little more in advance (phone, check, wallet, check) before lowering the roof. But in reality, it only takes 60 seconds for the roof to go up / down so it's more of a mild annoyance than anything else and the low profile is essential for some gates, bridges, trees ..... and gas mileage. So a small price to pay.
It's a big truck, which is worse than a small truck if you are in a tight space. But much better than a small truck when you want to live in it.
Generally, I think it fits a perfect spot in between a big MAN style box and a smaller van. I love all sizes, each has their benefit, but there is very little to touch the XP/Nimbl if you are looking for something within that bandwidth. The Nimbl/XP comes into its own if you want to travel and live in an agile vehicle. It's small enough to get around easily, even comparatively gnarly off road, but pop the roof and it's spacious and big enough to live full time comfortably (we were around 3.5 years full time). It's a pretty epic camper.
Hope that helps.