billgates: We went with the D28 in the end. Placed an order today and should arrive by Friday. Thanks @Stu & @timmmay for the recommendation.
@billgates what was the main deciding factor to get this over a P30 (or other more affordable model)?
billgates: @Paul1977 the biggest factors were 100m long, 50mm wider openings vs on the P30. 120mm deeper treads vs 80mm on the P30. The width of the steps is also 50mm wider than P30. We have created a huge storage area above the garage and also have installed a ducted aircon unit and separate ventilation system in the new build. Servicing it or replacing parts or even entire aircon unit would be possible with the D28 if it comes to that. Got the D28 for $1395 incl shipping instead of $1500.
@billgates great minds think alike. We're doing very similar with ducted heatpump and lossnay ventilator, and I also specifically had the attic space designed to allow easy access for this.
The Lossnay and heatpump/plenums (once broken down) should fit through the smaller hatch on the P30 if I worked it out right. It surprises me that most people don't seem to make an allowance for the possibility of having to replace a large ducted system or ventilator. They say you don't need to do this, but do they really think these units will last the life of the house?