Door panel sealant strip size?

[dvhttn]

My door panels need resealing and not being a fan of just 'squirting some silicon sealant' on them I was going to get some butyl strip to do it properly. However, I wasn't too sure about what strip width etc to get. I guess it doesn't make too much difference but is this Ebay item more or less right .... https://www.ebay.co.uk/itm/BOLT-ON-PANE ... 1226885203 .....? One thing I would be grateful for though is 'how long'? Rather, how long should the strip be for each door, bearing in mind I only want one join per door (at the top!!)? Without taking each panel off to measure them (from memory the channel for each strip takes a convoluted course) I can only approximate.

Ta in advance.